Southern California -- this just in

Babies have been hardest hit by whooping cough in California, according to new statistics released by the state Department of Public Health.

All nine deaths so far this year have been among infants under 3 months old. Among patients who are critically ill with the disease, babies have also been disproportionately hospitalized.

According to the data released late Wednesday, of 196 patients known to have been hospitalized with whooping cough in California, 74% were infants under 6 months old and most -- 57% -- were under 3 months old.

Whooping cough is often spread to babies by parents, siblings, aunts, uncles and grandparents and other adults. Because infants do not begin vaccinations until they are 2 months old, health officials for months have been pleading for anyone who expects to be in contact with babies -- especially pregnant women -- to get vaccinated.

“There are a lot of people who aren’t fully immunized,” said Dr. Jonathan Fielding, director of the Los Angeles County Department of Public Health. “People with respiratory conditions and cold-like conditions should not have contact with small infants.”

Whooping cough is spreading among adults too, but many of those cases aren’t reflected in the state’s numbers because the disease is often not diagnosed in adults.

Cases of whooping cough, or pertussis, continue to tick upward in California. State data as of Tuesday show that California has had the most cases of whooping cough since 1955, with 4,017 confirmed, probable and suspect cases reported so far this year.

The latest figure surpasses the number of cases reported in 1958 in California, when 3,837 people were sickened with the severe bacterial disease. This year marks the highest number of whooping cough cases in California since widespread vaccination efforts began in the 1940s and '50s.

[Updated 1:45 p.m.: State officials said the current rate of infection is 10.3 cases per 100,000 people, the highest incidence since 1962 when the state reported a rate of 10.9 cases per 100,000.]

Health officials also released demographic information showing that 77% of the hospitalized infants under 6 months old were Latino, as were eight of the nine fatalities.

Ken August, a spokesman for the California Department of Public Health, said health officials believe very young Latino infants are overrepresented in hospitalized cases because Latino babies “are more likely to live in larger households, per census data,” giving the infants more opportunities to be exposed to someone with whooping cough.

Infants under 6 months old are among the most susceptible to whooping cough because they are too young to have received the three inoculations needed to give them considerable protection from the disease. Vaccination guidelines call for shots at 2, 4 and 6 months.

August said the rates of immunization for Latino children are high and after 6 months of age hospitalization rates drop for Latinos. State data show that, overall, whites are the most likely group to be affected by whooping cough.

In addition to high rates of whooping cough in infants under 6 months old, state data also show high rates among children ages 7 to 9 and people ages 10 to 18 years.

Cases of whooping cough seemed to surge this summer, according to the state data, with more than 700 cases reported in May and close to 1,000 cases each in June and July.

The state numbers on pertussis cases ultimately may climb. Some diagnoses may come later, and confirmed cases are not always immediately relayed by counties to Sacramento.

A news conference to discuss the state's whooping cough epidemic, as well as the upcoming flu season, is scheduled for 11 a.m. Thursday in Sacramento.

Fielding, the health officer in Los Angeles, said he didn’t know whether whopping cough cases had crested locally. He said he anticipated more diagnoses as children return to school this month and as doctors pay more attention to a disease some have erroneously believed was relegated to the history books.